While the electromagneto-mechanical actuator of the present invention may be applied to any useful purpose, it has particular advantage in positioning the head for magnetic computer data storage of the type where a reading head is positioned radially over the desired track of a memory disk.
In the past various types of actuating means for positioning such a head have been employed. One of the first types employed for this purpose comprised electrical servomotors but these had a relatively slow response in the order of 100 milliseconds.
Another type involved an on-off solenoid-controlled electrohydraulic actuator and had a faster response in the order of 60 milliseconds but this type had the disadvantages of oil seepage which produced oil mist to deposit as films of oil on the magnetic disks, and also many parts were involved which made the cost relatively high. While more sophisticated analog hydraulic devices can be employed to produce a faster response time, these devices still suffer from the other disadvantages of the hydraulic type.
The current trend in this art is to use a voice coil electromagnetic translational actuator which has a response time of about 40 milliseconds but has other undesirable characteristics such as being physically relatively large involving a permanent magnet weighing about fifty pounds, having a high permanent magnet flux field from which flux leakage gives potential data erasure problems, requiring the voice coil to be fixed to the reading head and therefore makes for a difficult voice coil mechanical suspension, having the permanent magnet structure separately mounted from the voice coil, possessing unreliability of the lead-out wires from the bobbin of the voice coil which has a relatively long stroke of two inches resulting in excessive flexing of these wires, requiring a relatively high electrical current to develop a large force inasmuch as the device was direct acting, and having poor coil heat dissipation capability which led to unreliability.